Preparation And Properties Of Yolk-shell S-GO Composite As Cathode Material

Lithium-sulfur battery is expected to be next-generation battery. However, it still has serious problems that prevent it from being widely used. Researchers have made efforts to optimize the batteries, including designing structure and improving properties of cathode materials. Yolk-shell structure is a good choice to solve these problems. Some researchers have prepared yolk-shell TiO2-S or yolk-shell polymer-S composite as cathode materials of Li-S batteries. With the help of shell and the void space, inner part of the composite can be protected well.The general method to prepare yolk-shell Li-S cathode composite is encapsulating sulfur and then partially dissolving or heating to make void space. Because dissolving or heating can easily destroy the structure and isn’t easy to be controlled, it is not efficient in protecting sulfur. In this work, we aimed to encapsulate hollow sulfur with graphene oxide (GO), achieving yolk-shell S-GO composite directly.We prepared sulfur using wet-chemical reaction, researched the effect of conditions, and controlled the morphology of the sulfur particles. We have prepared uniform submicron sulfur particles with hollow structure. And we chose GO as the shell material and wrapped it onto sulfur by controlling ionic strength of the solution at room temperature. The composite showed good electrochemical properties. The details are as follows:(1) By adding different amount of PVP, we can get sulfur particles with different morphology. PVP can help sulfur particles to be uniform in size, and make the particles hollow. More PVP can lead to a more hollow structure. We succussfully prepared some uniform hollow sulfur particles with a diameter of 500nm.(2) Temperature, PVP molecular weight, concentration, the amount of HCl and the kind of acid can all influence the morphology of sulfur particles. To prepare hollow sulfur particles, the conditions are as follows:under 30℃,100ml 0.04M sodium thiosulfate solution,0.2g PVP,0.67ml HCl, reacting 2 hours under magnetic stirring, suction filtration and washing.(3) When sulfur particles with hollow structure were wrapped by GO, there was void space inside the shell without further treatment. The prepared yolk-shell S-GO composite got its first discharge capacity of 575.98mAh/g at 0.2A/g, and the composite with much GO retained 61.9% of the capacity after 100 cycles under lA/g. These results proved good electrochemical properties of the yolk-shell S-GO composite.